Assessment of the relationship between standard probe and implantable fiber measurements of cortical bone blood flow: a canine study

The Use of the Implantable Doppler Probe as a Blood Flow Monitoring Device in Clinical Settings: A Narrative Review of the Evidence

OBJECTIVES

In the past decade, the implantable Doppler probe has been studied widely as a blood flow-monitoring device in reconstructive and transplant surgical specialities. Its utility as an effective postoperative monitoring technique is still debatable, with no clear guidelines in clinical practice. Here, we mapped the current evidence on the usefulness of the implantable Doppler probe as a blood flow-monitoring device. The objective was to present an up-to-date assessment of the benefits and limitations of using implantable Doppler probes in clinical and experimental clinical settings.

MATERIALS AND METHODS

We conducted a literature search using the Cochrane Library and Healthcare Databases Advanced Search and using implantable Doppler probe, transplant, graft, and flap as key words. The search yielded 184 studies, with 73 studies included after exclusions. We evaluated, synthesized, and summarized the evidence from the studies in tabular form.

RESULTS

There is clinical equipoise regarding the effectiveness of implantable Doppler probe as a flow sensing technique. The main reason is the lack of information and gaps in the evidence regarding the benefits and limitations of using implantable Doppler probes in clinical practice.

CONCLUSIONS

The implantable Doppler probe has the potentialto be used as an adjunctpostoperativeblood flow-monitoring device. However, keeping in view of technical limitations, its signals should be interpreted alongside traditional clinical assessment techniques to determine the patency of microvascular anastomosis. Although evidence in this review will inform clinical practice in transplant and reconstructive surgical specialties, a prospective randomized controlled study with a larger patient cohort is required to evaluate the effectiveness of this probe in clinical settings.

Continual measurement of intramedullary blood perfusion with laser Doppler flowmetry in intact and ostectomized tibiae of rabbits

Blood flow is important for the healing of bone fractures. Until now, however, there have been no publications on the daily, continual measurement of intramedullary blood perfusion using laser Doppler flowmetry (LDF) in the conscious animal. In this study, a model for the daily, continual measurement of intramedullary blood perfusion by LDF and the temperature near the cortex both in intact and ostectomized tibiae in the conscious rabbit is described. The probes for blood perfusion and temperature measurement were implanted permanently at three different localizations into the right tibia of 10 adult New Zealand White rabbits. The probes were held in place by a bilateral, single-plane external fixator. In five of these animals, a midshaft tibial ostectomy was created in order to simulate a fracture. Intramedullary blood perfusion and temperature were measured daily over 49 days.

While in intact tibiae no significant ( P > 0.05) differences were found in blood perfusion readings taken at various time points, for mean values or for blood perfusion over time, in ostectomized tibiae the differences were significant: various time points ( P = 0.0056), mean values ( P = 0.0034) and blood perfusion over time ( P = 0.0337). Blood perfusion readings at the centre probe were elevated compared with those at the proximal and distal probes.

Thus, a revascularization in the ostectomy gap during the fracture healing was proven by means of the LDF. No influence of the blood perfusion on the temperature in the ostectomy area could be determined during healing of the ostectomy. The described model seems suitable for the continual measurement of intramedullary blood perfusion both in intact and ostectomized tibiae in the conscious rabbit.

Immunofluorescence imaging as a tool for studying the pharmacokinetics of a human monoclonal single chain fragment antibody

We have used immunofluorescence imaging to study binding of a monoclonal antibody fragment to subcutaneously implanted human melanoma cells in nude mice. The data acquired using this nontraditional approach was then analyzed using standard pharmacokinetic methods to produce estimates of k(e) (0.06h(-1)), t 1/2 (16 h), mean residency time (23.4 h) and percent exposure of the antibody to the tumor (40%). To our knowledge this is the first time standard pharmacokinetic analyzes have been conducted on immunofluorescence imaging data. The combination of this novel imaging technique and standard pharmacokinetic analytical methods should prove to be a useful tool for comparing the properties of antibody fragments in animal models.

Dynamic measurement of bone blood perfusion with modified laser Doppler imaging

Although the mechanisms are not clearly defined, blood flow may play an important role in moderating skeletal adaptation. Most techniques currently available to measure blood flow in bone are time-consuming and require destruction of the tissue, but laser Doppler technology offers a less invasive method. The present study assessed whether laser Doppler perfusion imaging could detect changes in perfusion in cortical bone. By use of modified laser Doppler perfusion imaging with an adjustable, incorporated, near infrared-laser gain photodetection system, perfusion of blood in the mid-diaphyseal tibial cortex of New Zealand White rabbits (n = 5) was measured before, during, and after occlusion of the femoral artery. During occlusion, perfusion decreased 69% compared with control levels; removal of the arterial clip caused flux values to return to near normal. Laser Doppler perfusion imaging provides a two-dimensional image related to blood flow, and the results of this pilot study suggest that it may be an effective technique for imaging in vivo dynamic changes in perfusion in cortical bone.